[Patent Document 1] JP-A-2000-276856
[Patent Document 2] JP-A-2000-278645
As information technology including information processing and information communications becomes more advanced, the need arises for reusing information that has been previously created and edited. Such a need increases to a great degree the significance of the technology used for information storage. Until now, information recorders utilizing various media exemplified by magnetic tapes and magnetic disks have been developed and used widely.
Among such information recorders, HDDs (Hard Disk Drives) are auxiliary storage devices of a magnetic recording system. The drive unit of an HDD houses a plurality of magnetic media each serving as a recording medium, and those magnetic media are motor-driven and rotate at a high speed. The magnetic media are each plated with a magnetic substance including iron oxide and cobalt chromium, or coated with a thin film thereof.
The surfaces of magnetic media are subjected to rotation scanning by the magnetic head in the radius direction. As a result of such scanning, the magnetic media are magnetized to a level equivalent to data so that data writing or reading becomes possible.
The hard disks are already quite popular for use with personal computers as their standard external storage devices. Such hard disks are used to install various types of software needed to activate computers including operating systems (OSs), applications, or others, or to store any created or edited files. The HDD is generally connected to the main unit of a computer through a standard interface exemplified by IDE (Integrated Drive Electronics) or SCSI (Small Computer System Interface). The storage space of the HDD is managed by a file system such as an FAT (File Allocation Table) serving as a sub system for the operating system.
The HDDs have been recently increased in capacity, and such capacity increase is favorably leading to expansion of the range of applications. Not only serving conventionally as auxiliary storage devices for computers, the HDDs are becoming available for storing various contents as hard disk recorders that store any broadcast-received AV contents.
Exemplified here is a case of using a hard disk as an auxiliary storage device for a computer to discuss the physical format or the data reading/writing operation of the hard disk.
The hard disk is formed with, concentrically, a plurality of “tracks” as data storage partitions. These tracks are numbered in sequence starting with 0, from the outermost rim of the disk toward the inside. The larger number of tracks on the disk surface leads to the larger storage capacity of the corresponding recording medium.
The track is then divided into “sectors”, each of which is a recording unit. The sector is used as a basis for a data reading/writing operation that is generally performed to/from the disk. Although the size of the sector varies depending on the medium type, generally, the sector of the hard disk has 512 bytes. The track having the longer perimeter is provided with the larger number of sectors. This is aimed to uniformalize the recording density among the tracks to a substantial level with a consideration given to the usage efficiency of the recording media. Such a system is referred to as “Zone Bit Recording”.
With such zone bit recording adopted, the recording density can be almost uniformalized among the tracks, but disadvantageously, no such uniformalization can be derived for the data transfer speed. The track locating closer to the inner radius of the disk has the lower data transfer speed.
Assuming that an HDD has such a structure that a plurality of recording media are overlaid therein on one another concentrically, it means that the tracks sharing the same number among the media are forming the cylindrical shape. This is referred to as “cylinder”. The cylinder is assigned the same number as its corresponding track number, and is numbered in sequence starting with 0 from the outermost rim of the cylinder. A head is plurally inserted among the recording media, and those heads are always activated as a piece to move among the cylinders.
For addressing any target sector, a possible format is CHS, which is a format to access any desired data through specification of PBAs (Physical Block Addresses) on the disk in order of C (Cylinder), H (Head), and S (Sector).
The problem with such CHS, however, there are limitations on specifiable CHS parameters on the side of the main unit of a computer that operates as a host for the HDD. Due to such limitations, no provision can be made for hard disks increasing in capacity. This is the reason why LBA (Logical Block Address) has been adopted, with which cylinder numbers, head numbers, and sector numbers (CHS) are represented by logical consecutive numbers referred to as LBA, starting from number 0.
In a conventional HDD, for data reading/writing to/from a medium through an access made thereto, the magnetic head first scans the medium to find a track including a target sector. This is referred to as a “seek” operation of the magnetic head. Thereafter, to reach the target sector on the track, the medium rotates until the target sector comes right beneath the magnetic head. This is referred to as “rotational delay”.
The larger disk capacity increases the track density, thereby narrowing the track width to a considerable extent. In view thereof, for correct data writing and reproduction, high precision is required for positioning of the magnetic head. For the purpose, the servo technology has been adopted to enable positioning of the magnetic head always in the track center. Specifically, the tracks are each written with a signal called “servo pattern” at given intervals, and those servo patterns are read by the magnetic head to check whether the magnetic head is locating at the track center. Such writing of servo patterns is done with great precision during the HDD manufacturing process. The servo regions are each written with a signal for head positioning, a cylinder number, a head number, a servo number, and the like.
Many of the conventional HDDs are provided with their own interface such as IDE or SCSI for establishing a connection with a computer. Such an interface defines a command set, which is used for disk drive control exercised by the main unit of the computer. As the basic operation for such control, specifications are made which LBA number is indicating the head sector, and how many sectors are to be accessed.
As a result of such specifications, the HDD side becomes allowed to access from the specified head sector, and during such an access procedure, a lookahead sequence can be created with a prediction what sector is to be accessed next.
Such a lookahead operation has the premise that sector allocation has been so completed with respect to a series of data that no break is observed in continuity of addresses from one sector to the next. Generally, such sectors showing no break in continuity of addresses are observed in the consecutive head numbers or track numbers.
The lookahead operation works effectively for data reading in a case where any large data is written in a row on the recording media.
Considered here is a case where a storage region is considerably fragmented, and any large data is thus broken up and the resulting small data pieces are scattered across a plurality of locations. If this is the case, the lookahead operation at the time of data reading does not work effectively as expected because it performs data designation erroneously. Such a phenomenon may be resulted from the fact that the HDD side is not grasping the file structure to be handled by the host side, e.g., main unit of a computer, asking for data reading/writing.
Considered here is also a case where the sector prediction that has been made beforehand is found wrong by a new access request coming from the host side. If this is the case, the disk drive does a seek operation with respect to the track of the sector including the data in request. Once tracking is done, the disk drive waits for the target sector to become accessible, resulting in the seek time and latency time.
Storage of the lookahead data is performed as much as the data buffer capacity allows. If the sector prediction is found wrong consecutively or intermittently, any unused old data on the data buffer is discarded in order of storage. What is more, during the lookahead operation, no seek start-up is available.
As is evident from the above, the seek time and latency time, and the ineffective lookahead operation are all blamed for the delay of seek start-up, resulting in time loss. Moreover, the ineffective lookahead operation is the reason for data loss.
For betterment, to shorten both the seek time and the latency time, the disk drive of a general type has been structured to have the higher disk rotation speed. This is because no regularity is observed for the amount and structure of data to be handled on the host side exemplified by a computer, resulting in a difficulty in achieving improvement by the access method. Increasing the rotation speed for the disk as such is, however, considered unfavorable and causes trouble in view of power consumption and storage capacity.
Moreover, many of the external storage systems such as HDDs perform error correction on a sector basis. Herein, one sector has generally 512 bytes. In this manner, any random errors to be generated in the sectors can be subjected to error correction, but no error correction is available for the random errors if those exceed an error correction range, or burst errors. With this being the case, any possible reading errors have been reduced to a certain level or lower by a retry operation or others.
Another problem here is that such a retry operation requires a re-read procedure with a wait for a full disk rotation. This causes a further delay for the data reading time.
Exemplarily in systems dealing with AV contents, the transfer speed is often required to be high for HD (High-Definition) reproduction, special reproduction, or the like, and thus even if any uncorrectable reading errors occur in the sector(s), no retry operation may be possible in terms of time. If this is the case, under the present circumstances, there is no choice but to go through the procedure with no error correction performed, consequently degrading the reproduction quality.
The above-mentioned Patent Document 2 discloses the technology using information about importance of data blocks for recording. Based on the information, any data blocks indicated as important are selectively subjected to the retry operation, but the remaining data blocks are not, for example.
The above-described Patent Document 1 discloses the technology also using information about importance of data blocks for recording. Based on the information, any data blocks indicated as important are selectively increased in their error correction capability, but the remaining data blocks are only provided with the correction capability of normal level, for example.
Such technologies serve properly to some extent especially in systems dealing with AV contents or others, but are not effective enough in terms of eliminating the need for the retry operation and correcting errors, whereby the demand therefor has been increasing.
What is more, if any disturbances such as vibrations are caused during reading of the AV contents, errors occur more than not having such disturbances. This consequently increases the amount of data that is not subjectable to error correction, thereby degrading the reproduction quality after all.
With some disturbances, errors tend to occur more often immediately after a seek operation is through. As a possible reason therefor, the disturbances may problematically lengthen the time needed to derive on-track, consequently resulting in errors.
Thus occurred errors are classified into random errors and burst errors. With no disturbance, the errors occur randomly with no exception, but with some disturbances, the randomness is increased and burst errors occur sometimes.
With this being the case, as exemplary error correction, a correction procedure may be executed to inter-sector in addition to a correction procedure applied to intra-section. In this manner, the correction procedure becomes available not only for random errors but also for burst errors. However, the problem still remains, and as the disturbance level becomes higher, the sector(s) eventually become error-uncorrectable, and the number of such sectors will show a further increase.
When the disturbance level is high, the above-mentioned time needed to derive on-track will not be uniform to a greater degree. This means positioning of the head sector for data reading becomes difficult immediately after a seek operation is through.
Another possible reason for more errors at the time of data reading is deterioration with time. Deterioration of SPM (Spindle Motor) or VCM (Voice Coil Motor) will result in the similar phenomenon as above when any earlier-written data is to be read out.
Any errors caused by this type of disturbances immediately after a seek operation is through surely adversely affect the data quality, the access time, and the transfer speed. Accordingly, there have been demands for taking measures against errors caused as such.